The present invention is in the field of tire retreading apparatus, and relates to improvements in both an apparatus and method used for retreading tires. In particular, the invention relates to rasp blades, and an improved assembly and method of use of such blades on tire rasp hubs for buffing away the tread on worn tires.
The conventional process by which tire casings are retreaded is to buff away the worn tread, repair any damage that may be required in the casing after buffing, bond a new tread to the casing by a selected vulcanizing process, and then cure the rubber so as to harden and shape it into the desired tread design.
In order to buff and remove the worn tread, the tire casing is mounted on a buffing machine and inflated. A hub assembly, comprising a hub core having a large number of toothed rasp blades mounted thereon, is then rapidly rotated such as on a motor driven shaft, and the peripheral surface of the casing bearing the worn tread is forced against the rotating rasp blades to loosen, tear and grind off the excess rubber and roughen the remaining surface sufficiently so that the buffed surface of the casing can form a sufficient bond with the new replacement rubber tread in the vulcanizing process. Each tire size has a predetermined crown width, profile and radius and the casing must be buffed to the particular shape, size and texture to receive a new tread that ensures proper tread-to-road contact. Buffing of the worn tread is, therefore, a critically important operation of the retreading process affecting the quality, performance and safety of the retreaded tire.
Rasp blades of the prior art comprise numerous configurations and shapes, with a preferred type having teeth of essentially dove-tail shape projecting from the outer working edge. Individual teeth have a notch cut out from the center of the periphery or working edge of the tooth to form a series of substantially xe2x80x9cYxe2x80x9d (or dove-tail) shaped teeth defined by cutouts of partly circular shape. The notch formed in each tooth divides it into halves. Each half of a given tooth is offset to opposite sides of the plane in which the blade lies, thus creating a primary cutting edge to one side of the blade body followed by a laterally spaced buffing edge for each tooth. As the rasp hub is rotated, the primary cutting edge and the buffing edge prepare the surface of the casing to a texture necessary and desirable for bonding to a new rubber tread.
A typical tire buffing hub assembly which includes rasp blades has the form of a hub defined by interconnected front and back cylindrical end plates having mounted there between arcuate or quadrant-shaped rasp blades stacked in four (or more) separate arrays around the perimeter of the hub. Each rasp blade of any one stack is separated from adjacent blades of the stack by spacers, the stack being secured in position between the end plates by support pins. The hub assembly is mounted on a drive shaft, and a The hub assembly is mounted on a drive shaft, and a bolt holds the end plates together, sandwiching the rasp blades, thus allowing for dismantling of the hub for purposes of blade replacement, such as when the teeth become worn or are broken. The stacks of blades may be inclined relative to a plane perpendicular to the axis of rotation of the hub; and the stacks may be alternated in this inclination or offset. That is, the blades of one stack may be inclined toward one end of the hub and an adjacent stack inclined toward the opposite end of the hub.
Many blades of various configurations and shapes used on tire rasp hubs, with all of the blades in a given hub having generally the same shape, size and distribution of teeth. For instance, any two adjacent blades in a stack may have identical secondary and tertiary configurations and the teeth of one blade may be substantially laterally aligned with the teeth of an adjacent blade. This arrangement is typically facilitated by using identical blades throughout and fixing each blade of a stack in a xe2x80x9cname downxe2x80x9d (or xe2x80x9cface downxe2x80x9d) direction, whereby the manufacturer""s name appears on only one of the two opposed faces of the blade and indicates the direction in which the name side of all blades of that stack are to face. Where this technique is not employed, some other means for facilitating the stacking of the blades in a commonly aligned direction is used.
All of the teeth on each blade are symmetrically disposed along the working edge of the blade. For instance, the tooth (or partial tooth) closest to one end of the blade is located the same distance from that end as the tooth closest to the other end is located from that other end. Thus, the blades and configuration of teeth remain the same even if the blade is reversed and the xe2x80x9cnamexe2x80x9d sides of adjacent blades face each other.
There have been suggestions to xe2x80x9cstaggerxe2x80x9d the teeth of adjacent blades to provide an improved buffed surface for better adhesion to the tread after treating the tread-receiving outer surface of the casing. By using a tire rasp assembled with staggered teeth according to this invention, worn tire tread may be buffed away from a casing at a rapid rate while developing minimum amount of heat that might otherwise adversely affect the texture of the buffed surface needed for suitable retreading. Such suggestions include U.S. Pat. No. 3,102,325 of Hemmeter, and Australian Patent Application No. 58,291/99 of Anthony Collins. However, both suggested approaches requires xe2x80x9cback to backxe2x80x9d stacking of the blades in loading a hub.
The present invention is directed to a rasp blade for a tire buffing machine adapted to be mounted on a conventional rotary hub which typically includes disc-shaped end mounting plates and a plurality of cylindrical mounting pins (normally 2 or 3 pins) pressed into one of the end plates. The mounting pins extend parallel to the axis of rotation of the hub and serve to mount the blades between the discs to form a rasp assembly which is then mounted to a driven shaft.
Each blade includes a curved blade body having mounting apertures adapted to be received on the mounting pins, and an outer, working edge on which the teeth are formed. The entire blade is formed from a stamping which makes it economical to manufacture. After the blade is stamped out, forward and rear segments of each individual tooth are displaced in opposite lateral directions relative to the plane of the blade. The teeth are arranged on the working edge of the blade in side-by-side relation and in uniform pitch (i.e. spacing).
The body of the blade includes a mounting aperture for each pin located on the one end disc of the hub. Two or three mounting pins may be used, and the blades have a corresponding number of mounting apertures. For purposes of illustration, it will be assumed that three such mounting pins are used.
The body of the blade thus includes three mounting apertures. According to the present invention, one or two of the mounting apertures are duplex mounting apertures. This means that the same opening has two separate locations for receiving one of the mounting pins. The two locations are offset laterally by an amount related to the pitch of the teeth such that when the blades are mounted all xe2x80x9cface upxe2x80x9d (or face down) on the hub, the cutting teeth of one blade are staggered relative to the cutting teeth of adjacent blades when viewed from the side so long as the mounting pin (or pins) is received in alternate ones of the openings of the duplex mounting aperture.
One advantage of the present invention is that all of the blades in a given quadrant of the hub can be mounted in the same orientation. This permits the operator to conveniently load blades in a rotary manner (that is, assembling all blades of a given rank in the assembly) or to load each quadrant of blades before going to the next quadrant, according to the preference of the operator. The invention also eliminates xe2x80x9cflippingxe2x80x9d of the blades when loading a hub, as required in systems in which the blades are mounted in xe2x80x9cback-to-backxe2x80x9d relation. Thus, the present invention reduces the amount of handling of the blades during assembly by the operator. Staggering the teeth is believed to produce more favorable conditions of buffing and a surface which forms an improved bond with the tread. In addition, staggering the teeth extends the life of the blade.
There are other features and advantages of the present invention which will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals are used to refer to like parts in the various views.